This invention relates to a semiconductor device which is provided with a positioning pattern for accurately cutting fuse elements formed on semiconductor chip surfaces by laser beam irradiation.
In analog semiconductor integrated circuit devices, there is known a laser trimming method for adjusting analog characteristics. For example, a description of such a method is made in Japanese Patent Laid open No. H5-13670. An integrated circuit is two-dimensionally patterned on a semiconductor wafer, and thereafter measurements are mad of various integrated circuit electric characteristics in a wafer state. Then fuse elements provided in interconnections are selected to adjust analog characteristics and cut by laser beam irradiation. The laser trimming method such as this can make adjustments of the integrated circuit analog characteristics into desired characteristics through selectively cutting the fuse elements. A positioning pattern is provided on a surface of the semiconductor wafer in order to irradiate a laser beam onto predetermined fuse elements. FIG. 3(a) is a plan view of a conventional positioning pattern, FIG. 3(b) is a sectional view of the conventional positioning pattern, and FIG. 3(c) is a diagram showing a variation in the light reflection amount where the positioning pattern is scanned over by irradiating a light beam along a C-C' line direction. The conventional positioning pattern comprising, as shown in FIG. 3(a), a so-called theta mark 301 provided in a scribe line area 203 to perform comparatively rough positioning in a semiconductor wafer rotating direction, and an X-direction trimming mark 302 and Y-direction trimming mark 303 for accurately positioning one by one semiconductor integrated circuit chips 201 placed in repetition. The theta mark 301 is desirably in a featured form different from that of the pad area 202 in the semiconductor integrated circuit chip 201 such that automatic recognition can be made.
Although a .GAMMA.-form was shown in the example in FIG. 3(a), another form may be satisfactory provided that it is in a featured form and recognition is easy to perform.
As shown in FIG. 3(b) the conventional positioning pattern is formed by a rectangular aluminum film 105 on a silicon-oxide first insulation film 102 provided on the silicon substrate 101. If a light beam is scanned over along a direction of a line C-C' in FIG. 3(a), a light reflection pattern as shown in FIG. 3(c) is obtained due to high reflectivity of the aluminum film 105. High light reflection amount is exhibited on the aluminum film 105, while the portion having no aluminum film 105 becomes low in light reflection amount. The position as a reference for trimming is grasped using a part where the light reflection amount varies between the high light reflection amount and the low light reflection amount. The positional relationship between the positioning pattern and the fuse element formed by a polysilicon film of the integrated circuit is determined during design. Accordingly, by irradiating a light beam onto the positioning pattern to detect a position where the light reflection amount varies, a coordinate of a desired fuse element is calculated. By irradiating laser to that site, the fuse elements can be selectively trimmed.
In the conventional laser trimming, however, the fuse elements and the positioning pattern are formed by different thin films, making possible to perform accurate positioning. Where a reference position is detected by a positioning pattern that is an aluminum pattern and then laser trimming is made on the polysilicon thin film as a fuse element, there occurs mis-alignment in laser irradiation area 32 with respect to the fuse element 31 as shown in FIG. 14 due to mis-registration occurring in the semiconductor process between the aluminum pattern and the elements formed by a polysilicon thin film. The laser irradiation area 32 is in an energy distribution of a Gaussian distribution, and low in energy intensity at a laser irradiation end. Consequently, if there is a mis-registration between the polysilicon film patterning and the aluminum film patterning during the wafer process, there arises a problem that stable cutting of the fuse elements becomes impossible. Incidentally, reference numeral 33 denotes burning in the underlying layer, and 34 denotes a portion left uncut of a fuse.
Also, in the conventional method the laser trimming positioning patterns are often placed in the scribe line area between the semiconductor integrated circuit chips. The scribe line area is a cutting allowance used for scribing (cutting) the semiconductor wafer. If there exist many films in this area, the dicing cutter edge might be damaged during dicing process, raising a problem that dicing process throughput is lowered and in an extreme case the semiconductor integrated circuit chip is damaged due to improper dicing.
Therefore, it is an object of this invention to provide a semiconductor device in which the fuse elements for the semiconductor chips can be accurately positioned and trimmed. Furthermore, it is an object of the present invention to enhance the trimming positioning accuracy thereby enabling reduction in size of the fuse element areas and hence cost.
It is another object to provide a semiconductor device with which no trouble is encountered in the dicing process by reducing the laser trimming positioning pattern area occupied in the scribe line area or introducing the laser trimming positioning pattern in the semiconductor integrated circuit chip.